1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 3: ANALYSIS
This exposure information will be linked to the ecological effects information described in
the next section to estimate potential risks to terrestrial and aquatic receptors in the Risk
Characterization.
3.2 Ecological Effects Characterization
The Ecological Effects Characterization is used to evaluate adverse effects that may result
from varying concentrations of stressors and to link these effects to the assessment
endpoints and ecological conceptual site model.
Effects data that were reviewed and evaluated consisted primarily of site-specific toxicity
and bioaccumulation bioassays for aquatic receptors. In addition, literature and toxicological
reviews were used to supplement the effects data for terrestrial receptors. These effects are
described in the following section and are used to compile a stressor-response profile that is
linked to the exposure profile developed in the previous section to estimate potential risks in
the Risk Characterization (Section 4).
3.2.1 Ecological Response Analysis
To assess the effect of site contaminants on ecological receptors, several toxicity bioassays
and bioaccumulation tests were conducted using environmental media (sediments, pore
water, and surface water) collected from various focused and random sample sites. Bioassay
results were used to calculate no observed effect concentrations (NOEC), lowest observed
effect concentrations (LOEC), effect concentrations for 50 percent of test organisms (EC 50 ),
and lethal concentrations for 50 percent of test organisms (LC 50 ) for chemicals detected in
sediments, pore water, and surface water. These results were further refined by conducting
statistical regression analyses on the sediment and pore water results. Information gathered
on effect levels was compiled into the stressor-response profile description (Section 3.2.2).
3.2.1.1 Toxicity Bioassays
Toxicity bioassays were conducted to establish site-specific effect levels for sediment, pore
water, and surface water. The intent of the bioassays was to simulate future post-restoration
conditions (e.g., flooding). Some of the tested sediment samples required hydration or
salinity adjustment before bioassays could be conducted. The possibility that hydration or
salinity adjustment of those samples might not accurately reflect the eventual sediment
chemistry or bioavailability was considered. It was estimated that a preliminary test to
experimentally determine the necessary incubation time would require several months,
which were not available because of the time constraints of the project. The approach used
represented the best available option and is presented in Appendix F. In addition,
uncertainties related to the bioassay methodologies are presented in Section 4.2.
Quality control evaluations included mortality in controls, responses of test organisms to
reference toxicants, water quality measurements, and specific issues related to
sample-specific manipulation required for toxicity testing including sample hydration and
salinity adjustment for the bioassays, which are discussed as part of the complete bioassay
report (see Appendix F).
SAC/143368(003.DOC) 3-25 ERA REPORT
7/31/02